How to get index of an object with documentListener?

I have 2 lists displayed vertically in a JFrame. Lets say list A is an ArrayList<CustomTexField> and list B is an ArrayList<JLabel>.

I want to "update" the elements of list B that matches the same index of elements inside list A with the value from the CustomTextField.

I've tried adding document listener, but don't know how to calculate the index.

@Override
    public void insertUpdate(DocumentEvent e) {
        try {

            listB().get(INDEX).setText(e.getDocument().getText(0, e.getDocument().getLength()) + "");

        } catch (BadLocationException e1) {
            e1.printStackTrace();
        }

    }

I have also created a method inside CustomTexField class that saves the index when its created but don't know how to 'read' it from e.getDocument()

EDIT: UPDATED TITLE

via Chebli Mohamed